1. Field of the Invention
The present invention relates to a reproduction apparatus and method for reproducing data recorded on an optical disk, and in particular to a reproduction apparatus and method for efficiently reading data from defective locations on an optical disk.
2. Description of the Related Art
A reproduction apparatus that reproduces data recorded on an optical disk reads the data in units of RUB (Read Unit Block) which is the minimum recording unit on the optical disk.
In this type of reproduction apparatuses, the data read out of a specific RUB on the optical disk may be lost due to failure in decoding the error correction code (ECC) for that data. ECC decoding may fail due to defects on the disk surface, such as scratches, dust, fingerprint stains, and minute bubbles produced when the optical disk was molded.
In reproduction apparatuses in the related art, to prevent the data loss due to such defects, parameters are set for reproduction processing and ECC decoding is attempted by applying the parameters to the data read out of the disk. Usually, these parameters can be changed depending on the types of defects to improve the data readout performance.
For example, Japanese Unexamined Patent Application Publication No. 2006-286112 describes a reproduction technique for setting an optimal parameter by determining the presence/absence of a defect and determining the kind of the defect on the basis of the minuteness and size of the defect.
In addition to the reproduction technique described in Japanese Unexamined Patent Application Publication No. 2006-286112, another reproduction technique is in practical use in which a plurality of parameters used for various types of defects are prepared in advance and ECC decoding is attempted by sequentially changing the parameters. In this reproduction technique, the parameters prepared in advance are arranged in a specific order in advance and ECC decoding are retried by changing the parameters in this order until ECC decoding is successfully completed.
The data reproduction technique in such a reproduction apparatus in the related art will now be described more specifically. In this type of reproduction apparatus, data is read sequentially from the RUBS arranged, for example, in an annual ring-like structure on the recording medium. In the first reproduction processing (referred to below as “normal reproduction processing” where appropriate) for the data read out of a specific RUB, a parameter is set to its initial value and ECC decoding is attempted for this data. If the ECC decoding is not successfully completed in the normal reproduction processing, the reproduction apparatus changes the parameter setting and retries the reproduction processing (referred to below as “retried reproduction processing” where appropriate).
Parameter values used in the retried reproduction processing are listed in a parameter table. For example, a plurality of parameter values are listed in the order of application for ECC decoding. More specifically, for example, a parameter value effective for scratches on the disk is listed first in the parameter table and a parameter value effective for dust is listed second. A parameter value effective for bubbles on the disk is listed third and a parameter value effective for fingerprint stains is listed fourth.
If ECC decoding fails in the normal reproduction processing, the reproduction apparatus sequentially changes the parameter values by looking up the parameter table and repeats the retried reproduction processing until ECC decoding is successfully completed. Once ECC decoding is completed, data is read out of the next RUB and ECC decoding for this data is attempted in the normal reproduction processing. Since a defect often occurs in an extremely limited area on the disk, the parameter is reset to its initial value after ECC decoding is completed for a specific RUB.
As described above, in a related-art reproduction apparatus installed in a personal computer (PC) for example, if ECC decoding is not successfully completed in the normal reproduction processing, retried reproduction processing is repeated the allowed number of times to complete ECC decoding.
Suppose that a defect is present in a specific RUB and ECC decoding for the data read out of this RUB was successfully completed with the fourth parameter value in the parameter table, that is, ECC decoding was not successfully completed in the normal reproduction processing and was successfully completed in the fourth retried reproduction processing.
After ECC decoding for the data read out of a specific RUB is completed using the fourth parameter value, the reproduction apparatus resets the parameter to its initial value and reads data out of the next RUB and attempts ECC decoding for this data. In this manner, ECC decoding is attempted independently for the data read out of each RUB.
Suppose that, after an optical head of the reproduction apparatus has read data on the disk with a rotation, ECC decoding is attempted for the data read out of the RUB radially adjacent to the RUB where the retried reproduction processing was previously performed. If the current RUB is also defective and reproduction processing is retried, the type of defect in the current RUB is probably the same as the one in the RUB where the retried reproduction processing was previously performed, because a defect often extends over a plurality of radially adjacent RUBs. In this case, ECC decoding for the current RUB would probably be successfully completed if the fourth parameter value were used.